Koharu Rikka (小春六花) is a Japanese vocal developed and distributed by TOKYO6 ENTERTAINMENT in collaboration with AH-Software Co. Ltd., and was released as Standard and AI voice databases for Synthesizer V Studio in March 2021. She was formerly announced as a VOICEROID product, but was instead developed and released for CeVIO AI for speech at the same time as her Synthesizer V Studio voice databases. 
Her voice provider is Yoshino Aoyama, a Japanese voice actress.
Koharu Rikka is described to be a second-year student at Otaru Shiokaze High School. She's 160 cm tall and she has a teddy bear companion named Lakiston. The rest of her character is deliberately left open to interpretation.
Her birthday is May 16, the same day she was announced.
Koharu (小春) is derived from the word "koharubiyori" (小春日和), which literally translates to "little spring weather," but is more commonly referred to as an "Indian summer." Akasakov, the CEO of TOKYO6, mentioned in the AHS' 156th livestream that he chose this name for her because he wanted fans to be reminded of a soothing and relaxing spring day.
Rikka (六花) can be translated literally as "six flowers," but it also references snow. As the snow pseudonym is widely used in poetry written during the Song Dynasty, it's hoped that her name would help her appeal more to fans in China. 
Her name is rendered in kana as "コハル リッカ".
Rikka is a high school student with short silver hair. While her hair is pulled up into two small buns on either side of her head, the rest of her hair is not pulled up. She also has a small flower clip on the left side of her bangs. Her eye color is a soft blend of purple and red.
Rikka wears a standard school uniform - a grey top with a pink bow and a dark blue/white accented long sleeved jacket over it. She also wears a short, dark blue, pleated skirt, white knee-high socks, and pink/white shoes with a lavender bow on top of each.
Lakiston, her companion, is a stuffed bear with small black horns and black claws. It wears a green/white/blue bow and has small angel wings on its back.
- Lakiston - A stuff bear companion
- Hanakuma Chifuyu - fellow student & music club member at Otaru Shiokaze High School.
- Natsuki Karin - fellow student & music club member at Otaru Shiokaze High School.
- Koharu Rikka (VOICEROID2), Cancelled
- Koharu Rikka Talk Voice (CeVIO AI), March 18 2021
- Koharu Rikka Standard (Synthesizer V Studio), March 18 2021
- Koharu Rikka AI (Synthesizer V Studio), March 18 2021
- Koharu Rikka Standard Lite (Synthesizer V Studio), March 18 2021
- Koharu Rikka AI Lite (Synthesizer V Studio), March 18 2021
Koharu Rikka was planned to have live music performances, collaborations with other companies, and more.
Following a stream in February 2021, AH-Software announced a special campaign on Twitter allowing users to apply via DM to receive a physical copy of Synthesizer V Studio Pro and Synthesizer V Koharu Rikka AI Complete. The giveaway occurred on March 8 and ten prize winners were selected.
Rikka's first performance, "Koharu Rikka 1st LIVE!" would be held on April 22, 2022 at Harevutai in Ikebukuro.
- Koharu Rikka's Official Twitter
- TOKYO6 Entertainment Official Twitter
- TOKYO6 Entertainment Official Website
- AHS CEO Tweet confirming Koharu Rikka's Synthesizer V Development
- Announcement page
- Crowdfunding page